In the electrostatic painting of articles, for example automobile bodies, it is necessary to establish an electrical potential between a discharge atomizer and the automobile body so that the atomized paint particles become electrostatically charged for attraction to the electrically grounded automobile body. Establishing such an electrical potential typically requires an extremely high voltage source, typically in the order of 100 KV. This high voltage source creates, as a byproduct, an electrical field within a limited area about the discharge atomizer which tends to adversely effect all electronic instruments within the vicinity.
Paint, solvents, and the like, are typically supplied to the discharge atomizer using compressed air as the motive source. In most assembly line type automobile body painting facilities, the compressed air supply pressure will fluxuate a great deal. Thus, the rate of paint flow to the discharge atomizer will vary in response to the fluctuating air pressure unless a regulator valve is provided for regulating the flow rate of paint to the discharge atomizer. A constant dependable flow rate to the discharge atomizer, therefore, must be provided in order to ensure an evenly applied coat of paint to the automobile body.
To this end, flow meters are typically provided in a painting apparatus for measuring the flow rate to the discharge atomizer so that the regulator valve may be automatically readjusted to stabilize the flow rate to the discharge atomizer. Because of the electrical field created by the high voltage source, however, it has heretofore been difficult to achieve accurate readings of the measured flow rate from the meter since electronic recording data, when used in the vicinity of the electrical field, is adversely affected so as to yield unreliable results.
There is being marketed an optical sensing flow rate meter for optically measuring the rate of paint flow. However, this device is deficient in that a means for creating the light, e.g., a light bulb, is located within the housing of the flow meter. This means for creating light includes a supply of electricity, which, because the meter is located within the electrical field, is adversely affected by the electrical field resulting in inaccurate operation.